1. Field of the Invention
This invention relates generally to astronomical telescopes, and, more particularly, to techniques for balancing astronomical telescopes.
2. Description of Related Art
Astronomical telescopes are essential observing equipment for professional and amateur astronomers alike. Telescopes are available in a wide variety of optical types, including refracting, reflecting, and catadioptric systems, and with a wide variety of mounts, including altazimuth, equatorial, and spherical mounts.
Both altazimuth and equatorial mounts allow telescopes to rotate about two perpendicular axes. In a typical altazimuth mount, the axes allow up-down rotation of the telescope (altitude) and left-right rotation (azimuth). In an equatorially mounted telescope, the two axes are angled based on the observer's latitude, such that one axis allows rotation in declination (celestial “longitude”) and the other axis allows rotation in right ascension (celestial “latitude”). Equatorial mounts offer the advantage of single-axis tracking. With the mount aligned to a celestial pole (north or south), the mount can be counter-rotated in right ascension only to compensate for the earth's rotation. Equatorial mounts are generally equipped with clock drive units on their right ascension axes, which automatically provide the requisite counter-rotation to track celestial objects.
FIG. 1 shows an example of telescope that includes an equatorial mount 100 for carrying an optical assembly 150. This type of mount is known as a German equatorial mount. The mount 100 includes a declination (DEC) axis 110 and a right ascension (R.A.) axis 112. Internal shafts and bearings allow rotation of the mount 100 about both the declination and right ascension axes. The optical assembly 150 attaches to a clamp 120. The mount 100 may also include a counterweight shaft 122 and adjustable counterweight 124, for balancing the weight of the optical assembly 150. The mount includes an adjustment wedge 114. The wedge has a base 116, which is rotatably coupled to a tripod 118. Typically, the mount 100 also includes motor assemblies 126 and 128 for effecting controlled rotation of the mount in declination and right ascension, respectively. The mount 100 may also include a communications interface 130, for communicating with a hand controller or a computer for receiving commands to control the motors 126 and 128. The mount 100 may also include a DEC clutch 134 and an R.A. clutch 136 for locking the mount 100 in DEC and R.A. axes, respectively.
Balance of a telescope has conventionally been achieved by manually adjusting the position of the optical assembly 150 (e.g., forward or back along the clamp 120) and by adjusting the position of the counterweight 124. All desired accessories (e.g., eyepiece, camera, finder scope, etc.) are typically loaded prior to balancing. A rough balancing is first done by eye for safety. Then a more precise balancing is performed. To more precisely balance the telescope, the mount 100 is typically oriented with both axes 110 and 112 parallel to the ground. With this arrangement, the mount 100 may naturally tend to rotate one way or the other about each axis. An operator can then move the optical assembly 150 backwards or forwards along the clamp 120, and move the counterweight 124 in or out along the counterweight shaft 122, until balance about both axes is achieved.